Any disabling condition is bad, but there's a particular terror connected to the kind that destroys the body and leaves an alert mind locked inside. Stephen Hawking has spent much of his life inside just that kind of corporeal prison. The late Jean-Dominique Bauby described his own, similar experiences in the extraordinary memoir The Diving Bell and the Butterfly, a book he wrote one painstaking letter at a time by blinking his eye in alphabetic code.

But the lives of patients suffering from so-called locked-in syndrome might one day become a little less desolate. According to a small study just published in the Journal of Neural Engineering, a new technique may make it possible for people on the outside to communicate with these patients by, in effect, reading their minds. (See pictures of Asia's mental health centers.)

The brain is nothing if not a biological machine  one that works like any other machine, at least when it comes to temperature. Parts that are working harder than others become hotter than others, thanks to the additional flow of blood shunted their way. Engineer Tom Chau of the University of Toronto suspected he could take advantage of that fact.

Chau, the university's research chair in pediatric rehab engineering, has long been looking for ways to use residual physical cues like breathing patterns and heart rates to help locked-in children convey their needs. The brain was another natural avenue for communication, and Chau and Ph.D. student Sheena Luu figured out a way to test it.

They first recruited a group of nine healthy adults and presented each with a list of eight beverages, which they were asked to rate in appeal on a scale of 1 to 5. The investigators then outfitted each participant with a headband equipped with fiber-optic strands that projected infrared light through the scalp and skull and into the prefrontal cortex, a brain area critical for processing preference. Infrared imaging is typically used to detect heat, which is just what the researchers were looking for. The volunteers were shown pictures of different pairs of drinks from their original list and asked to mentally decide which one they liked better while Chau and Luu monitored their frontal-lobe activity.

"As activated areas of the brain receive more blood and more oxygen, the optical properties [of the brain tissue] change," says Luu. "This allows us to infer the pattern of activity beneath." As it turned out, they inferred very well. Blood flow was not a perfect predictor, but fully 80% of the time, the pattern on the brain monitor did suggest the preferences the subjects had indicated earlier.

Chau and Luu are not the first to experiment with a technique like this. In the terra incognita of cognitive research, brain-computer interfaces are increasingly common  but complicated. Typically, subjects have to be trained to use them and must rehearse a random, energy-intensive brain task like mentally singing a song in order to light up a pattern of brain activity that sends a signal to the researchers. The new technique extracts information much more directly by targeting the frontal lobe's preference functions. What's more, while other studies have required the subjects to activate their brains over and over again so that researchers could average the subtle changes in their scans across many trials, Chau and Luu's technique is precise enough that they needed to look only once. "This is a single-trial system," says Chau.

Still, there are bugs to overcome. Since strong dislike may excite blood flow as easily as strong like, it is important to first run a few preliminary infrared scans to determine the particular blood-flow signature of a person's brain, and then to calibrate the computer accordingly. That, however, is a relatively easy tweak, no more complicated than customizing voice-recognition software to individual users. "It's really just a matter of refining the algorithms," says Chau. "We envision this at the very least as a preference detector that allows people to direct their own care."

That may still leave locked-in patients a long, long way from the lives they lost. But it does represent an important step in the right direction.